The present embodiments relate to tissue property ultrasound imaging. Tissue is a viscoelastic material. Strain, shear, hardness, stiffness, or other property of tissue may be determined.
One tissue property or component of viscoelasticity is elasticity. Ultrasound imaging may operate in an elasticity imaging mode. U.S. Pat. Nos. 5,107,837; 5,293,870; 5,178,147; and 6,508,768 describe methods to generate elasticity images using the relative tissue displacement between adjacent frames. The tissue strain is determined in response to a stress applied to tissue. The stress is applied externally, such as by manual pressure or by acoustic pressure. Strain or strain rate are detected for generating an elasticity image. Shear velocity and relaxation time of tissue under stress may be determined. Altered stiffness regions may be identified. However, strain is relative or qualitative. For example, different amounts of applied stress result in different amounts of strain. The amount of applied stress may be unknown or difficult to accurately determine.
Pressure sensors may be used to determine the amount of manually applied pressure at the surface of the skin. However, pressure sensors may not be available or accurate for determining internal stress. Acoustic radiation force may be transmitted at a known amplitude. However, aberrations or other propagation errors may limit accuracy of determined stress applied at the internal tissue. Acoustic force information may not be available, or the amount of acoustic radiation applied to a patient may be limited.
Other parameters may be determined or estimated, such as modulus (e.g., hardness). Modulus may be quantitative, but may require additional transmissions or measurements. Such additional measurements may undesirably delay imaging.